NVIDIA GeForce GT 620M vs NVIDIA GeForce GT 640M LE

NVIDIA GeForce GT 620M

The NVIDIA GeForce GT 620M is an entry-level, DirectX 11 compatible graphics card that was announced in the first quarter of 2012 for laptops. Its core can be based on either the 40nm GF108 chip (similar to the GeForce GT 525M) or the new power-optimized 28nm GF117 chip with 64-bit or 128-bit DDR3 memory. Both architectures still stem directly from the Fermi generation.

It should be noted that the 28nm version of the GT 620M does not offer dedicated graphics ports and can therefore only be used in conjunction with Optimus.

Architecture

The GF117 is based on the optimized GF108 Fermi chip (GeForce GT 540M) and offers 96 shaders, 16 TMUs and 4 ROPs. Each shader core is clocked twice as fast as the rest of the graphics chip, a technique known as hot clocking. More detailed information on Fermi can be found on the GT 435M GPU page.

Performance

The 128-bit version of the GeForce GT 620M (with turbo) performs similarly to the older GeForce GT 540M due to their similar clock rates and core architecture. Therefore, modern and demanding games are playable in low to medium settings at 1366x768 pixel resolution. The rumored 64-bit version will likely suffer from the reduced bandwidth and offer slower performance in comparison.

Features

The shader cores (also called CUDA cores) can be used for general calculations with APIs such as CUDA, DirectCompute 2.1 and OpenCL. PhysX is theoretically possible, but the GT 620M is too slow to handle both PhysX and 3D rendering for modern games. 3D Vision is not supported according to Nvidia.

Nvidia claims that the power consumption of the Geforce GT 620M should be below that of the GeForce GT 525M due to the improved efficiency of the GF117 architecture.

NVIDIA GeForce GT 640M LE

The NVIDIA GeForce GT 640MLE is a mid-range, DirectX 11.1 compatible graphics card that was announced in the first quarter of 2012 for thin-and-light-laptops. It is a Kepler-based GPU built on the GK107 architecture and is manufactured in 28nm at TSMC. The graphics card uses a 128-Bit wide memory interface with DDR3-VRAM. A slower core clock of only 500 MHz differs the LE-model from a normal GT 640M. Watch out: Following rumors,there will also be a Fermi-based version (96 shaders, 762 MHz, DDR3/GDDR5, similar to 550M/555M) with a probably higher power consumption than the Kepler variant.

Architecture

The Kepler architecture is the successor to the Fermi architecture that first appeared in laptops with the GeForce 500M series. The GK107 Kepler core offers two shader blocks, called SMX, each with 192 shaders for a total of 384 shader cores that are clocked at the same speed as the processor core. Although more shader cores are available in the Kepler architecture as compared to the Fermi design, the Kepler shaders are still expected to be up to twice as power efficient. However, due to the missing hot clock of the shader domain, two shaders of a Kepler chip are as fast as one shader of a Fermi chip (the latter is clocked twice as fast). PCIe 3.0 is now supported by the mobile Kepler series and an optional Turbo mode can automatically overclock the Nvidia card by a theoretical 15 percent if the laptop cooling system allows it. The implementation of this boost mode is done in the BIOS, but it is ultimately dependent upon the manufacturer of the laptop.

Performance

Due to a clock speed of just 500 MHz, the gaming performance of the GeForce GT 640M LE is about 20 percent below the 640M. This is the same level as the GT 635M or the GT 555M. The performance is exceptionally good in shader-heavy DirectX 11 games and benchmarks. However, the 128-Bit memory interface can be a bottleneck if DDR3 graphics memory is used. Demanding games of 2011 like Battlefield 3 are playable in 1366x768 and medium settings.

Features

The improved feature set now includes support for up to 4 active displays. Furthermore, high resolution monitors of up to 3840x2160 pixels can now be connected using DisplayPort 1.2 or HDMI 1.4a if available. HD-Audio codecs, such as Dolby TrueHD and DTS-HD, can be transmitted via bitstream mode through the HDMI port. However, as most laptops will feature Optimus, the integrated GPU will likely have direct control over the display ports and may limit the feature set available by the Nvidia Kepler cards.

The 5th generation PureVideo HD video processor (VP5) is also integrated in the GK107 core and offers hardware decoding of HD videos. Common codecs such as MPEG-1/2, MPEG-4 ASP, H.264 and VC1/WMV9 are fully supported up to 4K resolutions while VC1 and MPEG-4 are supported up to 1080p. Two streams can be decoded in parallel for features such as Picture-in-Picture. Another novelty is the inclusion of a dedicated video encoding engine similar to Intel QuickSync that can be accessed by the NVENC API.

The power consumption of the GeForce GT 640M LE is similar to the older GeForce GT 520M. As a result, the Nvidia GPU is suited for thin-and-light laptops.